The present invention relates to a multicolor cathode-ray tube of the complex type which is used to constitute picture elements in a giant color display system.
Conventionally, giant display systems used, for example, as a display board at a sports stadium, an advertisement or other message display mounted on a roof top or a wall surface of a building, or an information display for highway service, are composed of an array of a large number of incandescent electric lamps which are selectively turned on and off. These display systems suffer from a number of drawbacks. In the case of incandescent electric lamps, light is obtained by heating a filament to or nearly to a white-hot temperature, and accordingly the light emitted therefrom is, respectively, white or orange in color. It is quite difficult to cause such an electric lamp to emit light having a large component, for example, in the blue or green range. Moreover, circuits for turning on and off or varying the current applied to the filaments of the lamps are required for modulating the brightness of each picture element. Moreover, such electric lamps have a very low frequency of response, lower than 10 Hz. Thus, there is a problem that the output color changes depending on the applied current. Also, there is a difficulty in producing images in half-tone colors. Still further, in such a giant display system, generally from several thousand to more than ten thousand 20- to 40-watt electric lamps are required, and accordingly there are problems regarding power consumption, heat generation, and the like.
With the intent of remedying these difficulties, the inventor has proposed the use of cathode-ray tubes as light sources for such a display system. In such an system, small cathode-ray tubes, each having a monochromatic fluorescent screen for emitting, for instance, red, green and blue light, are arranged to display a desired picture image. This system has advantages in that not only is the efficiency in converting electric energy into light energy improved to a large extent in comparison with the use of ordinary incandescent electric lamps, but also light of any desired color can be obtained. Thus, in the case where cathode-ray tubes are employed as light sources in a giant display system, it is apparent that the system provides advantages in performance, reliability, maintenance, power consumption, and the like, in comparison with the conventional display system employing incandescent electric lamps.
FIG. 1 illustrates an example of a cathode-ray tube used as a light source in a giant display system, which is an embodiment of a previous invention made by the present inventor. In the drawing, reference numeral 1 designates a cylindrical envelop, the interior of which is at vacuum pressure. This envelope 1 has at one end a faceplate 3 coated on the inside with a fluorescent layer 2. An electron gun 5 is provided at the other end thereof. for flooding the entire fluorescent screen 2 with an unfocused electron beam 4. Terminals 6 are provided for applying required voltages to various elements of the electron gun 5, and a stem portion 7 encloses the envelope 1. Reference numerals 8, 9 and 10 respectively designate a heater, a cathode, and a grid, which together constitute the electron gun 5.
Further description will be made with respect to the operation of the cathode-ray tube. With a negative voltage applied to the grid 10 relative to the cathode 9, a current is supplied to the heater 8 so as to heat the cathode 9 to cause the voltage of the grid 10 to approach the potential of the cathode 9 to thereby cause the cahode 8 to emit the electron beam 4 toward the fluorescent screen 2. The electron beam 4 is an unfocused beam confined within a predetermined solid angle (.theta.), the value of which is determined by various factors such as the diameter of a hole 11 formed at the center of the grid 10, the distance between the grid 10 and the cathode 9, and the anode voltage. This beam causes the fluorescent screen 2 to phosphoresce in a color determined by the type of phosphor.
Numbers of such cathode-ray tubes are regularly arranged with the screen side of each of tube forward, for example, as shown in FIG. 2. The cathode-ray tubes are arranged generally such that, in each row, one cathode-ray tube 22 emitting red light and an adjacent cathode-ray tube 23 emitting blue light are disposed between two cathode-ray tubes 21 emitting green light. In one example of such a display system, cathode-ray tubes each having a diameter of about 29 mm were arranged at intervals of about 40 to 45 mm. This interval was chosen to allow for waterproofing of the structure. The optimum viewing distance of the system is about 70 m or more in view of the clarity of the image as well as color reproduction, which distance is quite suitable for applications such as sports stadiums. However, for applications such as indoor displays or outdoor advertising displays, it has been found that the optimum viewing distance is about half that in the case of a sports stadium.
To reduce the optimum viewing distance, an embodiment has been proposed in which the fluorescent screen of each cathode-ray tube is divided into a plurality of sections, each of which emits light in a different primary color. FIG. 3 shows an example of such a cathode-ray tube 31, in which a fluorescent screen 2 is divided around the center into three fan-shaped sections which respectively generate primary color rays of red, green and blue. In the cathode-ray tube 31, for example, as shown in FIG. 4, individual electron guns 5a are provided for generating unfocused electron beams 4a directed to respective fluorescent screens 2a. In this case, the respective fluorescent screens 2a are supported on fluorescent screen targets 12a.